The invention is more particularly concerned with vehicle arresting devices of a kind comprising a flexible substrate intended to lie flat upon the ground when deployed with an array of upwardly-directed spikes attached to the substrate along a leading portion thereof (in the sense of the intended direction of approach of a vehicle to be arrested). The substrate in a device of this kind may be, for example, a panel of silk or other woven material, or it may be in the form of a net. One form of the latter kind of device is known from US Patent Application Publication no. 2006-0140715, the contents of which are incorporated herein by reference. The modus operandi of a successful arrest with a device of that kind is as follows. When a vehicle runs over the device the run-over spikes engage in its front tires and the net is caused to wrap around the front wheels, the portion of the net between those wheels being pulled tight under the vehicle so that the tension in the net prevents further rotation of the wheels and the vehicle is brought to a stop. In practice this occurs in a similar distance to an emergency stop as if the vehicle's brakes had been applied, and has the advantage that it can stop the vehicle without causing serious damage to the vehicle or injury to its occupants.
Devices of this kind have been tested in different grades aimed at the arrest of different classes of target vehicle but each have limitations for the arrest of a wider range of vehicles. For example a device made with a spike length and netting grade sufficient for the successful arrest of smaller, lighter vehicles such as passenger cars may be unable to arrest larger, heavier vehicles such as trucks for which longer, heavier spikes are required in order to achieve sufficient retention in the tires and a heavier grade of netting is required for sufficient strength to absorb the higher levels of kinetic energy involved in stopping a truck. More surprisingly, a device made with a spike length and netting grade sufficient for the successful arrest of the larger, heavier class of vehicle may not also be suited to the arrest of the smaller, lighter class of vehicle. In this respect, account must be taken of the relationship between tire diameter and spike length in order to achieve penetration when the tires encounter the spikes. For vehicles with small diameter tires, it may occur that long spikes are simply knocked over by the tires which have insufficient circumferential “reach” to roll onto the tips of the spikes. Furthermore, where spike penetration does initially take place, it may occur that the spikes are pulled out again if there is insufficient tire thickness and internal tire braiding to retain the heavier spikes against their inertia and the high centrifugal forces which are generated as they turn with the tires. This problem may also be exacerbated by the inertia of the heavier netting as the leading edge is picked up and the tire accelerates the net.
It is therefore an object of the present invention to provide a vehicle arresting device of the general kind indicated above but which is more suited to arresting a wider range of vehicle types than heretofore.